Article Figures & Data
Figures
- Figure 1.
Task design. A, Illustration of a whole experimental paradigm. For the fMRI study, participants (as player A) choose In or Out and reveal their belief probability that player B would choose Cooperation in the behavioral experiment. On different days, participants (as player B) decide to cooperate or defect in the fMRI experiment. For the tDCS study, in the behavioral experiment, participants (as player A) play the same task as the first part of the fMRI study. On different days, the tDCS and sham tDCS experiments are conducted. Participants play the trust game as player B while receiving either anodal or sham tDCS to the right DLPFC. The orders of the anodal and sham tDCS are counterbalanced across participants. B, Trust game task. After the green fixation period (2–5 s; Cue phase), a task condition is presented from 5 to 8 s (Choice phase), and participants are asked to press the Cooperate or Defect button (red and blue). A yellow fixation cross then appears from 6 to 12 s (Rest phase). C, The correlation coefficients between Reward, Guilt, and Inequity. There were no significant correlations (p > 0.05).
- Figure 2.
Behavioral results. A, The cooperation ratio in the first and second half in each study. The cooperation ratio was not different between the first and second half (fMRI study, p = 0.3505; tDCS study, p = 0.1747). B, Behavior. Plots show the rate that participants chose cooperation against reward, guilt, or inequity. C, The relationship between the belief probability, τA, and the rate that participants chose cooperation showed no significant correlation (p = 0.052).
- Figure 3.
fMRI and tDCS results. A, fMRI. Activity in the right DLPFC was correlated with guilt (p = 0.015, FWE), and the ventral striatum and amygdala with inequity (p < 0.001). B, tDCS. β(Guilt) and β(Inequity) are displayed for the tDCS and sham conditions separately. β(Guilt) in the tDCS condition was significantly higher than in the sham condition (*p < 0.05), but β(Inequity) and β(Reward) were not. Error bars represent SEs. C, Effect of tDCS on the frequency of cooperation. A significant positive relationship (r = 0.51, p = 0.019) between the difference (tDCS-sham) in β(Guilt) and difference (tDCS-sham) in the frequency of cooperation was seen.
Tables
- Table 1.
Activities correlated with the parametric modulator for size of Guilt during decision makinga
Region MNI coordinates (x, y, z) Voxel size (voxels) t value Right DLPFC 44, 34, 22 87 7.15 Right DLPFC 44, 12, 32 78 6.06 Left primary motor cortex −42, 4, 30 45 6.02 Right hippocampus 24, −26, 0 34 6.79 Right occipital lobe 22, −94, 6 4033 12.2 Left occipital lobe −12, −96, −4 3933 15.0 ↵aMNI coordinates (x, y, z) indicate the location of the peak correlation. The threshold is set at an FWE p < 0.05. The voxel size shows the number of suprathreshold voxels, and the t values are shown for the peak activation voxel.
- Table 2.
Activities correlated with the parametric modulator for size of Inequity during decision makinga
Region MNI coordinates (x, y, z) Voxel size (voxels) t value Right striatum 10, 8, 0 22 3.87 Right amygdala 16, −2, −12 12 3.57 ↵aMNI coordinates (x, y, z) indicate the location of the peak correlation. The thresholds are set at FWE p < 0.05 for the whole-brain analysis and at uncorrected p < 0.001 for region-of-interest analysis. The voxel size shows the number of suprathreshold voxels, and the t values are shown for the peak activation voxel. No suprathreshold cluster for the whole-brain analysis.
